Manufacture of aromatic sulfonic acids



United States Patent "cc MANUFACTURE OF AROMATIC SULFONIC ACIDS Richard F. Brooks, Webster Groves, Mo., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application December 6, 1956 Serial No. 626,593

5 Claims. (Cl. 260-505) This invention relates to the sulfonation of aromatic hydrocarbons and more particularly pertains to the manufacture of monosulfonic acids of aromatic hydrocarbons.

Aromatic sulfonic acids are manufactured in large quantities as intermediates in the synthesis of phenolic compounds and as intermediates in the synthesis of other organic chemical compounds. In the past, aromatic hydrocarbons such as benzene and naphthalene, toluene, xylene and other loweralkyl substituted benzenes as well as the alkyl substituted benzenes having long alkyl chains such as keryl benzene, dodecyl benzene and the like have been sulfonated to the corresponding monosulfonic acids by reacting the hydrocarbon in the liquid phase with a sulfonating agent such as sulfuric acid, oleum or sulfur trioxide. However, sulfonation of benzene and such other aromatic hydrocarbons as the lower alkyl substituted benzenes having 1 to 4 carbon atoms in the alkyl groups with sulfur trioxide as with use of oleurns is accompanied by the objectionable formation of large quantities of aromatic sulfones.

The formation of aromatic sulfones is objectionable since the sulfones represent the consumption of a sizeable portion of the aromatic hydrocarbon reactant. Furthermore, in the synthesis of phenols, the formation of phenyl sulfone, tolyl sulfone, xylyl sulfone and naphthyl sulfones not only consumes two moles of the aromatic hydrocarbon per mole of sulfone formed, but the sulfone does not react with caustic to form a phenate. The sulfones add an undesirable property to the sulfonic acid product which would carry over in the synthesis derivatives of the sulfonic acid. I i I In aliquid phase sulfonation of aromatic hydrocarbons with sulfur trioxide the quantity of sulfones formed has been reported to be as high as 30%, that is, the amount of sulfone formed represents the consumption of 30% of the aromatic hydrocarbon raw material. This is especially true in the sulfonation of benzene and toluene with sulfur trioxide for the sulfone formation can go as high as 30% and about 25% respectively. In the sulfonation of xylene the sulfone formation is not quite as high, attaining a maximum of about 8 to 10%.

Various methods have been proposed for the reduction of objectionable formation of sulfones in the reaction of an aromatic hydrocarbon with sulfur trioxide. It has been proposed, for example, to carry out the sulfonation reaction in the presence of a solvent such as chloroform or liquid sulfur dioxide. It has also been proposed to use a sulfur trioxide complex such as a complex with trioxane as a sulfonating agent. It has been proposed that various sulfone inhibitors be employed. As sulfone inhibitors there have been suggested alkali metal and alkaline earth metal sulfates, sodium sulfate apparently being the preferred inhibitor of this class. It has also been proposed that alkali metal and alkaline earth metal sulfonates be employed as the sulfone inhibitor. As sulfone inhibitors it has also been proposed to use lower saturated alkyl acids, especially those containing 2 to 8 carbon atoms. The amount of sulfone inhibitor suggested as satisfactory 2,889,360 Patented June 2, V1959:-

according to these prior processes has been about 10% or less by weight based on the weight of the aromatic compound to be sulfonated. However, as has been pointed out the use of a greater amount of the sulfone inhibitor is not deleterious to the sulfonation reaction except in some instances where the sulfone inhibitor itself becomes sulfonated and in these cases the use of larger quantities of inhibitor will consume large portions of S0 in sulfonating the inhibiting material. The use of large quantities of inhibiting material such as the alkali metal or alkaline earth metal sulfonates, while not having a deleterious effect on the sulfonation step, does, of course, present a problem of removal of said amount from the reaction medium. If not removed, excess quantities of the sulfonates would be objectionable for many uses, as in the fusion step in the synthesis of phenol.

A new class of sulfone inhibitors for the sulfonation of aromatic compounds with sulfur trioxide has now been discovered. This new class of sulfone inhibitors comprises the acid modified bentonitic clays, that is, bentonitic clay which has been washed with a mineral acid to remove at least a portion of the sodium and/or calcium ions from the clay structure leaving in their place hydroxyl groups. Thus, the acid treated bentonitic clays useful in the process of this invention include the calcium bentonites which occur naturally and such bentonitic clays as montmorillonite. These bentonitic clays including the bentonites and sub-bentonites and the acid modifications or treatment thereof are well known to the art. The new class of sulfone inhibitors useful in the process of this invention will be referred to as acid treated bentonitic clay in the specification and in the claims.

More specifically, the process of this invention consists in reacting sulfur trioxide with a liquid aromatic hydrocarbon in the presence of an acid treated bentonitic clay at a reaction temperature as heretofore used, preferably under about 120 C., but more preferred reaction temperature being in the range of about 70 C(to about 90 C. There can be employed as the source of sulfur trioxide, oleum having an S0 content of 20% and above up to and including 100% S0 with no sulfuric acid being present. In the process of this invention there should be used at least about 2% by weight of the acid treated bentonitic clay based on the weight of the aromatic compound to be sulfonated. However, the use of'greater than 25% by weight and up to 60% by weightsor more is not deleterious as will hereinafter be il111strated.' How: ever, as a practical limitation it has been found that the use of an amount greater than about 30% by weight of the acid treated bentonitic clay offers little advantage and unreasonably complicates the removal of the acid treated bentonitic clay from the reaction mixture.

The following specific examples further illustrates the process of this invention.

Example I To suitable sulfonating apparatus there is added 284 parts by weight of a mixture containing benzene sulfonic acid, sulfuric acid, water and sulfones prepared by a previous mono-sulfonation of benzene with oleum of about 30% S0 This mixture contains 76.4% benzene sulfonic acid, 17.8% sulfuric acid, 4.8% water and 1.0% sulfones. This mixture is stirred and heated to about C. and there are added to the heated, stirred mixture about 60 parts by weight of sulfur trioxide and thereafter about 108 parts by weight of benzene and the remaining 108 parts by weight of sulfur trioxide are added simultaneously at equal weight rates. During the addition of the reactants the reaction temperature is maintained between about 77 C. and 83 C., and after all of the reactants are added, the resulting mixture is stirred and maintained at 80 to 85 C. for about one hour. The resulting reaction mixture contains 72% benzene sulfonic acid, 21.8% sulfuric acid, 0.4% water and 5.5% sulfones. From the composition of the starting mixture and the composition of the resulting reaction mixture it is determined that 18% of the benzene charged to the sulfonation reaction is converted to sulfones.

In contrast to the foregoing process in which no sulfone inhibitor was employed, the following examples employing the process of this invention utilize an acid treated bentonitic clay sold under the trademark Superfiltro Example II To suitable sulfonation apparatus there is charged 284 parts'by weight of the mixture described in Example I containing 76.4% benzene sulfonic acid, 17.8% sulfuric acid, 4.8% water and 1.0% sulfones. To this reaction mixture there is added parts by weight of acid treated bentonitic clay sold under the trademark Superfiltro The resulting mixture is stirred and heated to about 76 (1., 60 parts of sulfur trioxide are added, and when the temperature of the resulting mixture reaches 80 C., 112 parts by weight of each of benzene and sulfur trioxide are added simultaneously at an equal weight rate. The addition of the reactants requires about 45 minutes. The reaction temperature during the addition of the reactants is held between 73 to 79 C. and thereafter maintained at 80 to 83 C. for about one hour. An analysis of the resulting reaction mixture shows that it contains 72% benzene sulfonic acid, 22% sulfuric acid, about 0.6% water and 4% sulfones. From the composition of the starting mixture and from the composition of the resulting reaction mixture it is determined that 12% of the benzene charged is converted by this process to sulfones.

Example III ,The process of Example II is repeated except that 30 parts by weight of the acid treated clay is added instead of the 5 parts. The reaction temperature during the addition of the reactants is maintained at a temperature between 72 to 78 C. and after the reactants are added the reaction is held for one hour at 80 C. From the analysis of the starting mixture and of the reaction product it is determined that about of the benzene charged is converted to sulfones.

In Example II the amount of acid treated clay is equivalent to about 3 grams per gram mole of benzene charged. In Example III the amount of acid treated clay is equivalent to about 21 grams per gram mole of henzene charged. The use of acid treated clays in larger proportions than illustrated in Examples II and III above does not produce substantially greater reductions in the sulfone inhibitor was employed demonstrates how through the use of a relatively inexpensive acid treated bentonitic clay the reduction of the excessive formation of sulfones in the sulfonation of benzene can be accomplished. In a similar manner, there can be suppressed the sulfone formation which would otherwise occur during the nuclear monosulfonation of anaromatic hydrocarbon such as toluene, xylene and other alkyl substituted benzenes, naphthalene and the like.

What is claimed is:

l. A method of preparing benzene monosulfonic acid which comprises reacting benzene and sulfur trioxide in the presence of at least 2% by weight of an acid treated bentonitic clay based on the weight of benzene.

2. A method of preparing benzene monosulfonic acid which comprises reacting at a temperature below about C. benzene and sulfur trioxide in the presence of at least 2% by weight of an acid treated bentonitic clay based on the weight of benzene.

3. A method of preparing benzene monosultonic acid which comprises reacting at a temperature below 120 C. substantially equimolecular proportions of benzene and sulfur trioxide in the presence of at least 2% by weight of an acid treated bentonitic clay based on the weight of benzene.

4. A method of preparing a lower alkyl benzene monosulfonic acid by the nuclear sulfonation of the benzene .ring which comprises reacting a lower alkyl benzene and sulfur trioxide in the presence of at least 2% by weight of an acid treated bentonitic clay based on the weight of lower alkyl benzene.

5. A method of preparing monosulfonic acids of aromatic hydrocarbons by the nuclear sulfonation of a benzene ring which comprises reacting sulfur trioxide with an aromatic hydrocarbon in the liquid phase and in the presence of at least 2% by weight of an acid treated bentonitic clay based on the weight of aromatic hydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS 2,688,633 Cohen Sept. 7, 1954 

1. A METHOD OF PREPARING BENZENE MONOSULFONIC ACID WHICH COMPRISES REACTING BENZENE AND SULFUR TRIOXIDE IN THE PRESENCE OF AT LEAST 2% BY WEIGHT OF AN ACID TREATED BENTONITIC CLAY BASED ON THE WEIGHT OF BENZENE. 